Method of texturing solar cell and method of manufacturing solar cell

ABSTRACT

Methods of texturing and manufacturing a solar cell are provided. The method of texturing the solar includes texturing a surface of a substrate of the solar cell using a wet etchant, and the wet etchant includes a surfactant.

This application is a Continuation of co-pending application Ser. No.12/411,942 filed on Mar. 26, 2009, which claims priority to and thebenefit of Korean Patent Application No. 10-2008-0027996 filed in theKorean Intellectual Property Office on Mar. 26, 2008, the entirecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field

Embodiments relate to methods of texturing and manufacturing a solarcell. 2. Description of the Related Art

Recently, as existing energy sources such as petroleum and coal areexpected to be depleted, interests in alternative energy sources forreplacing the existing energy sources are increasing. Among thealternative energy sources, a solar cell is a cell generating electricenergy from solar energy and has been particularly spotlighted becausethe solar cell uses abundant solar energy, does not cause environmentalpollution, and has a long life time.

The solar cell is divided into a silicon solar cell, a compoundsemiconductor solar cell, and a tandem solar cell, depending on a rawmaterial. The silicon solar cell has been mainly used in a solar cellmarket.

A general silicon solar cell includes a substrate and an emitter layerformed of a semiconductor and having different conductive types such asa p-type and an n-type, and electrodes formed on the substrate and theemitter layer, respectively. At this time, a p-n junction is formed atan interface between the substrate and the emitter layer.

When light is incident on the solar cell, a plurality of pairs ofelectrons and holes are generated in the semiconductor. The pairs ofelectrons and holes are separated into electrons and holes by thephotovoltaic effect, respectively, and the separated electrons and holesare called carriers. Thus, the separated electrons move toward then-type semiconductor (ex. the emitter layer) and the separated holesmove the p-type semiconductor (ex. the substrate), and then theelectrodes and holes are collected by the electrodes electricallyconnected to the emitter layer and the substrate, respectively. Theelectrodes are connected to each other using electric wires to therebyobtain an electric power.

A reflectance of the incident light on the semiconductor needs to bereduced so as to improve a conversion efficiency of the solar cell forconverting light energy into electric energy. For this, a method oftexturing a surface of the semiconductor has been used.

SUMMARY

In one aspect, there is a method of texturing a solar cell, the methodcomprising texturing a surface of a substrate of the solar cell using awet etchant, and the wet etchant includes a surfactant.

In another aspect, there is a method of manufacturing a solar cell, themethod comprising forming an emitter layer on a substrate having a firstconductive type, the emitter layer having a second conductive typeopposite to the first conductive type, texturing a surface of theemitter layer using a wet etchant, forming a first electrode contactingthe textured emitter, and forming a second electrode contacting thesubstrate, and the wet etchant includes a surfactant.

The wet etchant may be an alkaline wet etchant.

The alkaline wet etchant may be an etchant including an alkalinesolution of 0.5 wt % to 23.5 wt % and the surfactant of 0.01 wt % to 0.1wt % in pure water.

The alkaline solution may be at least one selected from the groupconsisting of the potassium hydroxide (KOH), sodium hydroxide (NaOH) andammonium hydroxide (NH4OH) and a mixed solution thereof.

The substrate may be a single crystal silicon substrate.

The wet etchant may be an acidic wet etchant.

The acidic wet etchant may be an etchant including the surfactant in anacidic wet etch solution of HF and HNO3.

The acidic wet etchant may be an etchant including a HF solution ofabout 5 wt % to 30 wt %, a HNO3 solution of about 29 wt % to 75 wt %,and the surfactant of about 0.1 wt % to 3 wt % in pure water.

The substrate may be a polycrystalline substrate.

The surfactant may be a fluorine-containing surfactant.

The texturing may include generating a plurality of air bubbles byreacting the wet etchant and the substrate, the bubbles adhering on asurface of the substrate, wherein an etchant rate of first portions ofthe surface on which the bubbles are adhered may be different from anetchant rate of second portions of the surface on which the bubbles arenot adhered.

The surface may be at least upper portion of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more apparent by describing preferredembodiments thereof in detail with reference to the accompanyingdrawings in which:

FIGS. 1A to 1D are cross-sectional view sequentially illustrating atexturing method of an upper portion of a substrate for a solar cellaccording to an exemplary embodiment of the present invention;

FIG. 2 is a graph showing reflectances measured in a substratemanufactured by FIGS. 1A to 1D and in a substrate manufactured by acomparative example;

FIG. 3 is a partial cross-sectional view of a solar cell according to anexemplary embodiment of the present invention; and

FIGS. 4A to 4G are cross-sectional views sequentially illustrating amanufacturing method of the solar cell shown in FIG. 3.

DETAILED DESCRIPTION

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the inventions invention are shown. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. Like reference numerals designate likeelements throughout the specification. It will be understood that whenan element such as a layer, film, region, or substrate is referred to asbeing “on” another element, it can be directly on the other element orintervening elements may also be present. In contrast, when an elementis referred to as being “directly on” another element, there are nointervening elements present.

Referring to FIGS. 1A to 1D and FIG. 2, a method of texturing an upperportion of a substrate for a solar cell according to an exemplaryembodiment of the present invention will be described.

FIGS. 1A to 1D are cross-sectional view sequentially illustrating atexturing method of an upper portion of a substrate for a solar cellaccording to an exemplary embodiment of the present invention and FIG. 2is a graph showing reflectances measured in a substrate manufactured byFIGS. 1A to 1D and in a substrate manufactured by a comparative example.

Referring to FIG. 1A, a substrate 201 for manufacturing a solar cell isprepared. The substrate 201 is a semiconductor substrate obtained byslicing a semiconductor ingot made of a semiconductor such as silicon.At this time, the substrate 201 is formed of single crystal silicon, butmay be formed of polycrystalline silicon.

In slicing the semiconductor ingot, damage portions 202 are generated ona surface of the substrate 201 and the damage portions 202 adverselyaffect an operation of the substrate 201.

Referring to FIG. 1B, a texturing process is performed to form aplurality concave-convex portions on surface portions, for example, onan upper portion of the substrate 201 using the wet etching. Thus, theupper portion of the substrate 201 has an unevenness surface. Before thetexturing process, for protecting an undesired surface (ex. a lowerportion) from the texturing, an etch protection layer (now shown) isformed on the undesired surface of the substrate 201 and then is removedafter the texturing process is finished. However, alternativeembodiments, the etch protection layer may be not formed.

In embodiment, an etchant for the texturing process uses an alkaline wetetchant including a surfactant. For example, the alkaline wet etchantincludes an alkaline solution of 0.5 wt % to 23.5 wt % and a surfactantof 0.01 wt % to 0.1 wt % in pure water.

In this embodiment, a potassium hydroxide (KOH) solution is used as thealkaline solution, but may be used at least one selected from the groupconsisting of the potassium hydroxide (KOH), sodium hydroxide (NaOH) andammonium hydroxide (NH4OH) and a mixed solution thereof.

The surfactant included in the alkaline wet etchant is afluorine-containing surfactant. An example of typicalfluorine-containing surfactants may be zonyl (FOS-100 manufactured byDuPont. The fluorine-containing surfactant has a function decreasing thesurface tension of silicon. Thereby, in texturing the substrate 201, thefluorine-containing surfactant improves a surface wetting ability of thealkaline wet etchant in an initial reaction between the surface of thesubstrate 201 and the alkaline wet etchant. The alkaline wet etchantdoes not include IPA (isopropyl-alcohol).

As described above, when the surface of the substrate 201 is etched bythe alkaline wet etchant, the damage portions 202 are removed. At thistime, an etch rate of the substrate 201 is varied based on a crystaldirection of the signal crystal silicon. For example, since an etch rateof (111) surface of silicon is later than that of (100) surface of thesilicon, the concave-convex portions 203 are formed on the surface ofthe substrate 201 by an etch rate difference between the (111) and (100)surfaces so that the surface of the substrate 201 is texted.

When the texturing process of the surface of the substrate 201 isperformed, as shown in FIG. 1C, a plurality of air bubbles 204 aregenerated in surface portions of the substrate 201 by the reaction ofthe surface of the substrate 201 and the alkaline wet etchant, and thegenerated air bubbles 204 are adhered on the surface of the substrate201.

The bubbles 204 adhered on the surface of the substrate 201 disturb anetching operation in the surface positioned under the bubbles 204 andthus an etch rate of the surface of the substrate 201 is varied basedwhether or not the bubbles 204 are adhered. That is, etch rates betweenportions (first portions) of the surface of the substrate 201 on whichthe bubbles 204 are adhered and portions (second portions) of thesurface on which the bubbles 204 are not adhered are different from eachother. A height difference of the concave-convex portions 203 formed onthe surface of the substrate 201 more increases by the difference of theetch rate due to the bubbles 204 as well as the different surface typeof (100) and (111), and thereby reflection amount of light on thesurface of the substrate 201 is largely reduced so that a reflectionreduction effect is improved.

An alkaline wet etchant for texturing a substrate according the priorart had included IPA having a low volatility point in an alkalinesolution, so as to improve the surface wetting. Thus, in the texturingprocess, since the volatilized IPA should be periodically filled formaintaining a predetermined IPA concentration, an inconvenience hasoccurred and it has been hard to obtain the substrate having a uniformtextured surface due to the concentration variation of IPA. However,since the alkaline etchant according to the embodiment does not includeIPA, it is not required to fill IPA so that an inconvenience reduces anda surface uniformly textured on the substrate is obtained.

In the embodiment, each concave-convex portion 203 formed on the surfaceof the substrate 201 has a pyramid shape, but the shape of theconcave-convex portion 203 may be varied.

Meanwhile, when the amount of the surfactant included in the alkalinesolution is less than about 0.01 wt %, it is difficult to obtain theconcave-convex portions 203 of a desired shape, not to have a sufficienttexturing effect.

On the contrary, when the amount of the surfactant included in thealkaline solution is more than about 0.1 wt %, the bubbles 204excessively occurs more than needed. Thus, the texturing time increasesand the surface of the substrate 201 is not normally etched.Accordingly, the texturing effect is not obtained.

For example, the texturing of the surface of the substrate 20 isperformed by immersing the substrate 201 in a bath including thealkaline wet etchant of about 90° C., in which the surfactant isincluded, for about 35 min. When the texturing of the substrate 201 isfinished, as shown in FIG. 1D, the substrate 201 has a textured surfacewith the concave-convex portions 203. At this time, the damage portions202 are removed in the texturing, as described. Accordingly, areflectance of incident light on the substrate 201 decreases.

According to the embodiment, after the surface of the substrate 201 istextured using the alkaline wet etchant included the surfactant, it ismeasured a reflectance of the textured substrate 201 and a graph A ofthe measured reflectance is shown in FIG. 2. In FIG. 2, a graph B is areflectance of a substrate textured according to a comparative example,and in the comparative example, an acidic wet etchant is used fortexturing the surface of the substrate.

The substrates used in the embodiment and comparative example werep-type single crystal silicon substrates of about 125 mm. In addition,the alkaline wet etchant according to the embodiment included asurfactant of about 0.32 wt % into a KOH solution of about 5.2 wt % andthe acidic wet etchant according to the comparative example included HFand HNO3.

The texturing was performed by immersing the substrates in a bathincluding the corresponding etchant of about 90° C. for about 35 min.

The graphs A and B of FIG. 5 were obtained by a reflectance measurementequipment (model name: Solidspec-3700) manufactured by SHIMADZU Corp.,and the reflectance measurement was performed at about 400 nm to 1100 nmthat is a waveform band contributing to the electric generation.

As shown in FIG. 2, the reflectance A according to the embodiment wassmaller than the reflectance B according to the comparative example inmost of the waveform band. That is, amount of reflected light on thesurface of the substrate reduced. Further, when a value of an averageweighted reflectance (AWR) based on the results shown in FIG. 2 wascalculated, the value of AWR was about 23% in the comparative example,but about 11.4% in the embodiment. According to the measure result ofthe values of AWR, when the surface of the substrate was textured byusing the alkaline wet etchant including the surfactant, it was knownthat the reflectance of light was largely reduced.

Next, a method of manufacturing a solar cell using the texturing methoddescribed referring to FIGS. 1A to 1D will be described with referenceto FIGS. 3 and 4A to 4G.

First, referring to FIG. 3, a solar cell manufactured using thetexturing method based on FIGS. 1A to 1D will be described.

FIG. 3 is a partial cross-sectional view of a solar cell according to anexemplary embodiment of the present invention.

Referring to FIG. 3, the solar cell 1 according to an exemplaryembodiment of the present invention includes a substrate 201, an emitterlayer 210, an anti-reflection layer 310 positioned on the emitter layer210, a plurality of first electrodes (hereinafter, refer to as “frontelectrodes”) (320) electrically connected to the emitter layer 210, asecond electrode 330 (hereinafter, referred to as “a rear electrode”)positioned on the entire rear surface of the substrate 201 andelectrically connected to the substrate 201, and a back surface field(BSF) layer 340 positioned between the substrate 201 and the rearelectrode 330.

In the exemplary embodiment, the substrate 201 is made of silicon of afirst conductive type, for example, p-type. When the substrate 201 has ap-conductive type, the substrate 201 includes impurities of a group IIIelement such as boron (B), gallium (Ga), Indium, etc. However, in analternative embodiment, the substrate 201 may have an n-conductive typeand may be made of polycrystalline silicon or amorphous silicon.Alternatively, the substrate 201 may be made of other semiconductormaterials than silicon. When the substrate 201 has the n-conductivetype, the substrate 201 may include impurities of a group V element suchas phosphor (P), arsenic (As), antimony (Sb), etc.

The emitter layer 210 is an impurity portion that has a secondconductive type opposite to the conductive type of the substrate 201,for example, a n-conductive type, and is positioned on the surface onwhich light is incident, that is, the front surface of the substrate201. The emitter layer 201 forms a p-n junction with the substrate 201.

The emitter layer 210 serves as a light receiving surface of the solarcell 1 and includes a plurality of concave-convex portions 220 on asurface by texturing an upper portion. Thereby, a light reflectance onthe upper portion of the emitter layer 210 is reduced. Further, since aplurality of incident and reflection operations of light are performedon the fine concave-convex portions 220, light is confined inside thesolar cell 1. Accordingly, a light absorptance increases and theefficiency of the solar cell 1 is improved.

When light is incident on the semiconductor substrate 201, electron-holepairs, which are charges are generated. At this time, the generatedelectron- hole pairs are separated into electrics and holes by abuilt-in potential difference generated by the p-n junction, and theseparated electrons move toward the n-conductive type and the separatedholes move toward the p-conductive type. Thus, when the substrate 201has the p-conductive type and the emitter layer 210 has the n-conductivetype, the separated electrons move toward the substrate 201 and theseparated holes move toward the emitter layer 210. Accordingly, theholes become major carriers in the substrate 201 and the electronsbecome major carriers in the emitter layer 210.

Because the emitter layer 210 forms the p-n junction with the substrate201, when the substrate 201 has the n-conductive type, the emitter layer210 has the p-conductive type. In this case, the separated electronsmove toward the substrate 201 and the separated holes move toward theemitter layer 210.

When the emitter layer 210 has the n-conductive type, the emitter layer210 may be formed by doping the substrate 201 with of impurities of agroup V element such as P, As, Sb, etc. and when the emitter layer 210has the p-conductive type, the emitter layer 210 may be formed by dopingthe substrate 201 with of impurities of a group III element such as B,Ga, etc.

The anti-reflection layer 310 made of silicon nitride (SiNx) or siliconoxide (SiO2) is positioned on a surface of the emitter layer 210. Theanti-reflection layer 310 reduces the reflectance of incident light andincreases a selectivity of a specific wavelength band, therebyincreasing the efficiency of the solar cell 1. The anti-reflection layer310 may have a thickness of approximately 70 nm to 80 nm. Theanti-reflection layer 310 may be omitted, if necessary.

The plurality of front electrodes 320 are spaced apart from each otherat a constant distance and extend in a direction on the emitter layer210. The front electrodes 320 are electrically connected to the emitterlayer 210.

The front electrodes 320 are made of at least one conductive metalmaterial. Examples of the conductive metal material may be at least oneselected from the group consisting of nickel (Ni), copper (Cu), silver(Ag), aluminum (Al), tin (Sn), zinc (Zn), indium (In), titanium (Ti),gold (Au), and a combination thereof. Other conductive metal materialsmay be used. Other conductive metal materials may be used.

The rear electrode 330 is positioned on the entire rear surface of thesubstrate 201 and electrically connected to the substrate 201.

The rear electrode 330 is made of a conductive metal material. Examplesof the conductive metal material may be at least one selected from thegroup consisting of Ni, Cu, Ag, Al, Sn, Zn, In, Ti, Au, and acombination thereof. Other conductive metal materials may be used.

The back surface field layer 340 is positioned between the rearelectrode 330 and the substrate 201. The back surface field layer 340 isan area heavily doped with impurities of the same conductive type as thesubstrate 201. For example, the back surface field layer 340 is a p+area. Potential barrier is formed due to an impurity concentrationdifference between the substrate 201 and the back surface field layer340, thereby distributing the electron movement to a rear portion of thesubstrate 201. Accordingly, the back surface filed layer 340 preventsthe recombination and the disappearance of the separated electrons andthe separated holes in the interface of the substrate 201 and the rearelectrode 330.

An operation of the solar cell 1 having the structure will be described.

When light irradiated to the solar cell 1 is incident on the substrate201 of the semiconductor through the anti-reflection layer 310 and theemitter layer 210, electron-hole pairs are generated in the substrate201 by light energy based on the incident light. At this time, since theupper portion of the emitter layer 210 has the textured surface with theplurality of concave-convex portions 220, a light reflectance on theentire surface of the emitter layer 210 is reduced. Further, a pluralityof incident and reflection operations of light by the textured surfaceare performed and thereby light is confined inside the solar cell 1.Accordingly, a light absorptance increases and the efficiency of thesolar cell 1 is improved. Further, since a reflection loss of theincident light on the substrate 201 is reduced by the anti-reflectionlayer 310, amount of the incident light more increases.

The electron-hole pairs are separated by the p-n junction of thesubstrate 201 and the emitter layer 210, and the separated electronsmove toward the emitter layer 210 of the n-conductive type and theseparated holes move toward the substrate 201 of the p-conductive type.The electrons moved to the emitter layer 210 are collected by the frontelectrodes 320 and the holes moved to the substrate 201 are collected bythe rear electrode 330. When the front electrodes 320 and the rearelectrode 330 are connected with electric wires (not shown), currentflows to thereby use the current as an electric power.

Referring to FIGS. 4A to 4G, a method of manufacturing the solar cellshown in FIG. 3 will be described.

FIGS. 4A to 4G are cross-sectional views sequentially illustrating amanufacturing method of the solar cell shown in FIG. 3.

Referring to FIG. 4A, impurities of a group IV element such as P arediffused or deposited in a substrate 201 made of p-type single crystalsilicon, to form an emitter layer 210. Before the formation of theemitter layer 210, a removing process of damage portions (not shown) ofthe substrate 201 that is generated on a slicing process of silicon maybe performed.

Referring to FIG. 4B, an etch protection layer 400 is formed on anothersurface of the substrate 201, on which the emitter layer 210 is notformed. At this time, the etch protection layer 400 is made of amaterial not reacting with an alkaline wet etchant. For example, theetch protection layer 400 may be made of silicon oxide (SiOx), etc.

Referring to FIG. 4C, the surface of the emitter layer 210 is etched bythe alkaline wet etchant included a surfactant, to perform a texturingprocess of the emitter layer 210. At this time, the alkaline wet etchantis an etchant including an alkaline solution of 0.5 wt % to 23.5 wt %and the surfactant of 0.01 wt % to 0.1 wt % in pure water.

The texturing process may be performed by immersing the substrate 201having the emitter layer 210 in the alkaline wet etchant of about 90° C.for about 35 min.

At this time, as shown in FIG. 4C, when the surface of the emitter layer210 reacts with the alkaline wet etchant, a plurality of air bubbles 204are generated on portions of the surface of the emitter layer 210 andthe bubbles 204 are adhered on the surface of the emitter layer 210. Anetch rate on the surface of the emitter layer 210 is delayed due to thebubbles 204, and thereby an etch rate on portions of the surface onwhich the bubbles 204 are adhered is different from that of the surfaceon which the bubbles 204 are not adhered. Accordingly, as shown in FIG.4D, the emitter layer 210 has the textured surface with a plurality ofconcave-convex portions 220.

At this time, a height difference occurred by an etchant rate differencebased on the bubbles 204 is added in a height difference by an etch ratedifference based on a crystal surface type such as (100) or (111),thereby more reducing the reflectance of light. In addition, aconcave-convex portion shape may be a pyramid shape.

In this embodiment, since the alkaline wet etchant does not include IPA,there is no inconvenience to fill IPA in the alkaline wet etchant.

After the texturing process of the emitter layer 210 is completed, theetch protection layer 400 positioned on the rear surface of thesubstrate 201 is removed.

Accordingly, as shown in the FIG. 4D, the rear surface of the substrate201 is not etched by the etch protection layer 400, to maintain a flatsurface.

Referring to FIG. 4E, an anti-reflection layer 310 is formed on theentire surface of the emitter layer 210 using a chemical vapordeposition (CVD) method such as a plasma enhanced chemical vapordeposition (PECVD) method. The anti-reflection layer 310 may be made ofsilicon nitride (SiNx) or silicon oxide (SiO2).

Referring to FIG. 4F, a front electrode paste 321 including Ag isapplied on predetermined portions of the anti-reflection layer 310 usinga screen printing method and dried at about 170° C.

The front electrode paste 321 may be made of at least one materialselected from the group consisting of Ni, Cu, Al, Sn, Zn, In, Ti, Au,and a combination thereof, instead of Ag.

Referring to FIG. 4G, a rear electrode paste 331 is applied on theentire surface of the substrate, on which the emitter layer 210 is notformed, using a screen printing method. The rear electrode paste 331includes Al, but may include at least one material selected from thegroup consisting of Ag, Ni, Cu, Sn, Zn, In, Ti, Au, and a combinationthereof.

Next, by sintering the substrate 201 at about 750° C. to 800° C., aplurality of front electrodes 320, a rear electrode 330, and a backsurface field layer 340 are formed to manufacture the solar cell 1(refer to FIG. 3).

That is, the front electrode paste 321 contacts with the emitter layer210 through the anti-reflection layer 310, and thereby the frontelectrodes 320 and the rear electrode 330 are completed. In addition,the back surface field layer 340, on which p-type impurities are dopedheavier than the substrate 201 is formed between the substrate 201 andthe rear electrode 330.

In an alternative embodiment, the front electrodes 320 and the rearelectrode 330 may be formed on desired portions using a CVD methodinstead of the screen printing method. At this case, the drying andsintering processes, etc. may be omitted.

In addition, in an alternative embodiment, there may be not necessary toform the etch protection layer 400 on the rear surface of the substrate201 in the texturing process. Thereby, the rear surface of the substrate201 as well as the surface of the emitter layer 210 is textured. At thistime, after portions of the textured rear surface of the substrate 201are removed to flat the textured rear surface, the rear electrode 330may be formed on the flat rear surface of the substrate 201, but therear electrode 330 may be directly formed on the textured rear surfaceof the substrate 201.

In FIG. 3, the textured emitter layer 210 is positioned on the lightreceiving surface, that is, the front surface of the substrate, but maybe formed on the rear surface of the solar cell 1, on which light is notincident. At this case, the surface of the emitter is not textured, tohave a flat surface, but the front surface of the substrate 201 istextured to have the concave-convex portions 220. The substrate 201 istextured by the same method as the texturing method described abovereferring to FIGS. 1A to 1D.

Next, short circuit current (Jsc), an open circuit voltage (Voc), a fillfactor (FF), and a photoelectric conversion efficiency (EF) measured inthe solar cell manufactured by the embodiment are shown in [Table 1].

In [Table 1], a solar cell according to a comparative example has thesame structure as that of the embodiment. However, as compared with theembodiment, an emitter layer of the solar cell according to thecomparative example is textured using an acidic wet etchant including HFand HNO3. In [Table 1], data of the comparative example is correspondedto short circuit current, an open circuit voltage, a fill factor, and aphotoelectric conversion efficiency, respectively.

TABLE 1 Photoelectric Short circuit Open circuit conversion current(mA/cm2) voltage (mV) FF (%) efficiency (%) Embodiment 34.6 625 78 16.86Comparative 33.7 625 78 16.38 example

As known from the measurement results of [Table 1], the short circuitcurrent of the solar cell according to the embodiment increased by about0.9 mA/cm2 and the conversion efficiency of the solar cell according tothe embodiment was improved by about 0.5%, as compared with thecomparative example. Accordingly, when the texturing of the solar cellwas performed by the alkaline wet etchant including the surfactant, thelight reflectance was effectively reduced to largely improve theefficiency of the solar cell

Next, a texturing method of an upper portion of a substrate of a solarcell according to another embodiment of the present invention will bedescribed.

In this embodiment, as compared with FIGS. 1A to 1D, except for a kindof etchant for texturing a substrate and a kind of substrate, theremaining elements are equal. Accordingly, the detailed description ofthe remaining elements is omitted.

In this embodiment, the etchant for texturing the upper portion is anacidic wet etchant including a surfactant in an acidic wet etchsolution. The acidic wet etch solution includes HF and NHO3. Thesubstrate is polycrystalline silicon

For example, the etchant of the embodiment is an etchant including a HFsolution of about 5wt % to 30 wt %, a HNO3 solution of about 29 wt % to75 wt %, and a surfactant of about 0.1 wt % to 3 wt % in pure water.

Thereby, when the substrate of the solar cell is polycrystallinesilicon, amount of the surfactant is more increased, as compared thatthe substrate is single crystal silicon, to improve the efficiency ofthe texturing.

A method of manufacturing a solar cell using the texturing method by theacidic wet etchant of this embodiment is similar to the method describedabove in reference to FIGS. 3 and 4A to 4G. That is, except that intexturing the surface of the emitter layer, the acidic wet etchantincluding the surfactant and the acidic wet etch solution of HF and HNO3is used, the method of manufacturing the solar cell is the same as thatshown in FIGS. 3, 4A to 4G, and the method of manufacturing the solarcell according to the embodiment is omitted.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed:
 1. A method of texturing a solar cell, the methodcomprising: texturing a surface of a substrate of the solar cell using awet etchant, wherein the wet etchant includes a fluorine-containingsurfactant.
 2. The method of claim 1, wherein the wet etchant is analkaline wet etchant.
 3. The method of claim 2, wherein the alkaline wetetchant is an etchant including an alkaline solution of 0.5 wt % to 23.5wt % and the fluorine-containing surfactant of 0.01 wt % to 0.1 wt % inpure water.
 4. The method of claim 3, wherein the alkaline solution isat least one selected from the group consisting of potassium hydroxide(KOH), sodium hydroxide (NaOH) and ammonium hydroxide (NH₄OH) and amixed solution thereof.
 5. The method of claim 2, wherein the substrateis a single crystal silicon substrate.
 6. The method of claim 1, whereinthe wet etchant is an acidic wet etchant.
 7. The method of claim 6,wherein the acidic wet etchant is an etchant including thefluorine-containing surfactant in an acidic wet etch solution of HF andHNO₃.
 8. The method of claim 7, wherein the acidic wet etchant is anetchant including a HF solution of about 5 wt % to 30 wt %, a HNO₃solution of about 29 wt % to 75 wt %, and the fluorine-containingsurfactant of about 0.1 wt % to 3 wt % in pure water.
 9. The method ofclaim 6, wherein the substrate is a polycrystalline substrate.
 10. Themethod of claim 1, wherein the texturing comprises generating aplurality of bubbles by reacting the wet etchant and the substrate, theplurality of bubbles adhering on a surface of the substrate, and an etchrate of first portions of the surface on which the plurality of bubblesare adhered is different from an etch rate of second portions of thesurface on which the plurality of bubbles are not adhered.
 11. Themethod of claim 1, wherein the surface is at least an upper portion ofthe substrate.
 12. A method of manufacturing a solar cell, the methodcomprising: forming an emitter layer on a substrate of a firstconductive type, the emitter layer being of a second conductive typeopposite to the first conductive type; texturing a surface of theemitter layer using a wet etchant to form a textured emitter; forming afirst electrode contacting the textured emitter; and forming a secondelectrode contacting the substrate, wherein the wet etchant includes afluorine-containing surfactant.
 13. The method of claim 12, wherein thewet etchant is an alkaline wet etchant.
 14. The method of claim 13,wherein the alkaline wet etchant is an etchant including an alkalisolution of 0.5 wt % to 23.5 wt % and the fluorine-containing surfactantof 0.01 wt % to 0.1 wt % in pure water.
 15. The method of claim 14,wherein the alkali solution is at least one selected from the groupconsisting of potassium hydroxide (KOH), sodium hydroxide (NaOH) andammonium hydroxide (NH₄OH) and a mixed solution thereof.
 16. The methodof claim 12, wherein the wet etchant is an acidic wet etchant.
 17. Themethod of claim 16, wherein the acidic wet etchant is an etchantincluding the fluorine-containing surfactant in an acidic wet etchsolution of HF and HNO₃.
 18. The method of claim 17, wherein the acidicwet etchant is an etchant including a HF solution of about 5 wt % to 30wt %, a HNO₃ solution of about 29 wt % to 75 wt %, and thefluorine-containing surfactant of about 0.1 wt % to 3 wt % in purewater.
 19. The method of claim 12, wherein the texturing comprisesgenerating a plurality of bubbles by reacting the wet etchant and thesubstrate, the plurality of bubbles adhering on a surface of thesubstrate, and an etch rate of a first surface of the substrate on whichthe plurality of bubbles are adhered is different from an etch rate of asecond surface of the substrate on which the plurality of bubbles arenot adhered.